The U.S. is dealing with a big outbreak of the mumps.
As of mid-November, there have been more than 2,900 cases.
Arkansas had 1,900, and Iowa has nearly 700.
A number of clusters are on college campuses, where close quarters help the virus spread faster.
Many students may also be losing immunity from their childhood vaccinations.
The outbreak is so serious, the CDC is considering recommending a third dose of the mumps vaccine.
